Field of the Invention
The present invention relates to an image forming apparatus.
Description of the Related Art
Conventionally, image forming apparatuses adopting an electrophotographic system, such as a printer and a copying machine, are widely used. In general image forming apparatuses, there are cases where paper deviates to one side during conveyance in a direction (hereinafter referred to as a paper width direction or a main scanning direction) orthogonal to a conveying direction due to factors including various types and properties of paper to be used, characteristics of components such as conveying rollers, and use environments such as temperature and humidity during the conveyance. Executing a printing process in such conditions problematically reduces printing position accuracy.
Accordingly, so-called registration rocking correction is conventionally made for adjusting the position of the paper in relation to an image. This correction is such that a widthwise deviation amount of the paper is detected by a deviation sensor, and the paper is moved widthwise based on the detection result while being pressed into contact with (held by) a pair of registration rollers. JP 2013-88627 A discloses an image forming apparatus that executes, after registration rocking correction, error processing for improved accuracy of paper deviation correction when a deviation amount of paper that is detected by a deviation sensor is equal to or more than a predetermined amount or determines an adjustment amount for subsequent deviation correction.
The image forming apparatus described in JP 2013-88627 A, however, has the following problem. In cases where the registration rocking correction is made, for example, with a rear end of the paper not passing through a bent portion present in a reversing path where the paper is reversed, sliding friction is caused between the paper and a guide plate due to stiffness of the paper. Recently, there is an increasing demand for feeding of thick paper through a production printer. However, the thick paper has greatly increased stiffness, so that the problem of sliding friction becomes prominent. When paper such as the thick paper is used, a rear end of the paper cannot follow a rocking motion due to increased sliding friction, and consequently, the registration rocking correction results in the paper skewing to a level that cannot be ignored. The image forming apparatus described in JP 2013-88627 A can improve the accuracy of the deviation correction because the deviation correction is performed a plurality of times. However, this apparatus problematically cannot correct the skew of the paper.